We have a dataset that gives us for each customer the entry and exit time of a departure lounge, and we would like to calculate what is the maximum occupancy of the lounge at any given time.

The full dataset contains more than 800,000 customers, the period of time is an entire year, and we want to understand the maximum occupancy for each 10min slot across the day, for 364 days in the year.

We thought of a Gantt chart with time in column (10min slots across the day), and individuals in rows, and the size of a bar would represent the time spent in the lounge. From this we would need to count the number of bars populating each slot, but we don't know how to calculate it.

We've attached a simplified dataset with 88 customers as an example. We'd be grateful for any ideas or suggestions.